Circuit arrangement for starting and operating hot-cathode electric discharge lamp



June 25, 1957 W. HARRISON CIRCUIT ARRANGEMENT FOR STARTINGAND OPERATINGHOT-CATHODE ELECTRIC DISCHARGE LAMP Filed Aug. 6. 1954 A Home y UnitedStates Patent CCUH ARRANGEMENT FOR STARTING AND OPERATING HOT-CATHODEELECTRIC DIS- CHARGE LAMP William Harrison, Preston, England, assiguor,by mesne assignments, to Siemens Brothers & Co. Limited, Lon don,England, a British company Application August 6, 1954, Serial No.448,279

1 Ciairn. (Cl. 315-98) This invention relates to circuit arrangementsfor starting and operating hot-cathode electric discharge lamps, and hasin view the provision of an improved circuit arrangement for thestarting and operating, from an alternating current source such asordinary alternating current supply mains, of a hot-cathode electricdischarge lamp having filamentary heated electrodes.

According to the invention, a circuit arrangement for the starting andoperating, from an alternating current source, of a hot-cathode electricdischarge lamp having filamentary heated electrodes is such that asregards its energization from the alternating current source the lamphas in series with it the whole of the winding of a firstautotransformer and has connected directly in parallel with it theprimary winding of a second autotransformer, and such that the windingof the second autotransformer has at each end a secondary portionconnected to supply heating current to the filament at the correspondingend of the lamp, and such that as regards its connection to thealternating current source a capacitor serving for power factorimprovement has in series with it a primary portion of the winding ofthe first autotransformer, whereby a surge of current through the saidcapacitor which occurs upon switching on produces a voltage surge whichis stepped up by the first autotransformer and applied to the lamp as astarting Voltage. After starting, the first autotransformer serves as aballast impedance, and the shunting of the second autotransformer by thedischarge path through the lamp reduces the heating current supplied tothe filaments. Such a circuit arrangement enables fluorescent lampswithout earthed stripes to be started in the so-called instant startmanner.

The nature of the invention will be better understood from thedescription of specific circuit arrangements in accordance with it whichwill now be given with reference to the accompanying drawing:

Fig. 1 of the drawing illustrates one form of circuit arrangementaccording to the invention for the starting and operating of ahot-cathode fluorescent electric discharge lamp from an alternatingcurrent supply, and Fig. 2 illustrates a slightly difli'erent form ofsuch a circuit arrangement.

Referring firstly to Fig. 1, the circuit arrangement illustratedincludes a first autotransformer 1, a second autotransformer 2, acapacitor 3, and a switch 4. Terminals 5 are connected to thealternating current supply, and 6 is the fluorescent lamp concerned. Thelamp 6 has in series with it the whole of the winding of the first autotransformer 1 and has in parallel with it a major portion 7,constituting a primary portion, of the winding of the secondautotransformer 2. The last-mentioned winding has at each end asecondary portion 8 connected to supply heating current to the filament9 at the corresponding end of the lamp 6. The capacitor 3 serves forpower factor improvement, and is connected to the alternating currentsupply terminals 5, when the switch 4 is closed, through a primaryportion 10 of the winding of the first autotransformer 1. As aconsequence of this manner of connection of the capacitor 3, uponswitching on by closing the switch 4 the resulting surge of currentthrough the capacitor produces a voltage surge which is stepped up bythe first autotransformer 1 and applied to the lamp 6 as a startingvoltage. After starting, the first autotrans former it serves as aballast impedance, and the shunting of the second autotransformer 2 bythe discharge path through the lamp reduces the heating current suppliedto the filaments 9.

In the case where the lamp 6 is an 80-watt hot-cathode fluorescentelectric discharge lamp and the alternating current supply is a 230-voltone, the first autotransformer 1 may be constituted by a tapped chokewith the tapping (connected to the capacitor) about one-sixth of theWinding away from the terminal connected to the supply, and thecapacitor may have a value of 7.5 microfarads.

Referring now to Fig. 2, the circuit arrangement illustrated in thisfigure is very similar to that of Fig. 1, the only difference being thatthe secondary portions 8 of the winding of the second autotransformer 2are included in the effective primary winding of this transformer,instead of being outside the primary winding as is the case in thearrangement of Fig. 1. The elements of Fig. 2 correspond to thecorrespondingly designated elements of Fig. 1.

What is claimed is:

A circuit arrangement for the starting and operating from an alternatingcurrent source of a hot cathode electric discharge lamp havingfilamentary heated electrodes, comprising terminals for connection tothe alternating current source, a first autotransformer, said firstautotransformer and the lamp being connected in series across saidterminals, a second autotransformer connected directly across the lamp,said second autotransformer having a primary portion and at each end asecondary portion, each secondary portion being connected across thefilament at one end of the lamp, a tapping on said firstautotransformer, and a capacitor between said tapping and the terminalof the source not connected to said first autotransformer.

References Cited in the file of this patent UNITED STATES PATENTS2,333,499 Warren Nov. 2, 1943 2,462,336 Ruff Feb. 22, 1949 2,565,234Ilker Aug. 21, 1951 FOREIGN PATENTS 618,256 7 Great Britain Feb. 18,1949

